The present invention relates to a semiconductor device, and more specifically, to a semiconductor device comprising of a Silicon-On-Insulator (SOI) substrate having cell/core regions and a peripheral region, which is formed to have the same structure as that of a conventional substrate to obtain a floating body effect.
A DRAM for performing a general storage process is manufactured with a bulk silicon substrate. A semiconductor device for performing a storage process has a cell structure including a transistor and a capacitor.
Due to high integration of semiconductor devices, the cell structure has become complicated, and it is difficult to secure electric characteristics of the transistor and the capacitor. As a result, a semiconductor device comprising a SOI substrate has been developed. A top silicon substrate of the SOI substrate is isolated from a bottom silicon substrate by an insulating layer so that the transistor form the top silicon substrate can obtain a floating body effect.
If electrons passing through a channel of the transistor increases, a current flowing is increased and a drain voltage is also increased. When the drain voltage is larger, collision of silicon molecules is increased in the drain region to increase silicon electrons and holes. In the case of a general bulk substrate, the holes are passed through a ground to increase a threshold voltage of the transistor. In the case of a SOI substrate, holes are accumulated in the top silicon substrate to obtain a floating body effect for generating a voltage. As a result, it is easy to regulate a voltage of the body, thereby improving an electric characteristic of the transistor. The semiconductor device can serve as a memory device without a capacitor.
A SOI substrate is used for a DRAM cell. In this case, a model parameter, which has been developed in a conventional DRAM technology, is changed to develop a new circumstance. As a result, the floating body effect is not required. Moreover, a developing period for the model parameter of the peripheral region where various circuits are irregularly formed would be increased which would also increase the cost.